The knife applicator disclosed in U.S. Pat. No. 4,033,271 is designed to slice cleanly through the subsoil with a minimum of soil disturbance while at the same time preparing the soil to receive and trap substances deposited by the knife. This action of the applicator in disturbing the soil to the minimum possible extent also encourages the soil to close the slit by its own inherent resiliency.
The applicator of the U.S. Pat. No. 4,033,271 has been proven to be extremely efficient at serving its intended functions. However, in some conditions, there is room for further improvement. For example, in fields where the subsoil is not seasonally tilled and turned over, such as those producing grass crops, alfalfa, or pastureland, there is frequently a massive root system existing below the surface of the ground which could benefit from periodic aeration and relief, as well as nutritional feedings, to avoid a root-bound condition. The subsoil in those instances requires more fracturing or shattering than might be possible with the knife of the U.S. Pat. No. 4,033,271.
Accordingly, one important object of the present invention is to provide an improvement on the knife applicator of the U.S. Pat. No. 4,033,271 which makes it more suitable for use in those fields where greater subsoil shattering is desired and root systems established by non-replanted surface crops could benefit from subsoil relief and cultivation, as well as the injection of growth-promoting substances. In this respect, the present invention contemplates maintaining most of the constructional and relational features of the knife unchanged from that disclosed in the U.S. Pat. No. 4,033,271 while modifying the oppositely projecting wings thereof such that the wings are significantly wider than in the prior knife, are thicker than the prior wings, and converge clear to the forwardmost point of the knife in order to achieve the intended benefits.
It has also been found that in some soils it may be more difficult to close the slit or slice produced by the moving applicator knife than in others; that is, in some soil conditions there may be a sufficient lack of inherent resiliency in the soil that the slit will not be as self-closing as in other soils. Accordingly, another important object of the present invention is to provide another embodiment of the knife having special closing fins above and behind the side wings of the knife that encourage the soil lifted by the wings to be directed back downwardly toward the bottom of the slit and to be tucked in behind the knife so as to close off the slit. The fins are strategically positioned so as to avoid a counter-productive boiling or squeezing action in the soil which might occur if the fins were directly above and overlying the wings, in which case the wings would be pushing up on the same soil that the fins were attempting to push down. The span of the fins from side to side exceeds that of the wings so as to further reduce problems tending to arise through counteravailing forces in the wings and the fins.